Electroluminescence occurs in semiconductor materials which are capable of emitting visible or near visible radiation when an electrical current passes through the semiconductor. Photoluminescence can also occur in these materials. If external light is used to excite the semiconductor, a characteristic wavelength of light is emitted. These characteristic wavelengths vary amongst different photoluminescent semiconductors and can be varied in a single semiconductor by doping the material. The dopant will ordinarily cause a shift in the wavelength of radiation emitted by the material.
Amongst the various studies on the luminescence of photo-stimulated or electroluminescent materials is "Luminescent Photoelectrochemical Cells", Streckert, H. H., Tong, J. and Ellis, A. B., J. Am. Chem. Soc., Vol. 104, No. 2, 1982, pp. 581-588. It is noted therein that the intensity of light emitted by electroluminescence and photoluminescence varies directly with the applied voltage. The efficiency of charge transfer and good electrical contact at the surface is also noted as important in the efficiency of the process.
U.S. patent application Ser. No. 480,471 filed on Mar. 30, 1983 discloses semiconductor electrodes having multicolor luminescence. These semiconductors comprise solid state solutions of three elements which vary in a vertically anisotropic manner. The preferred solid state solutions are of cadmium, sulfur and selenium.
U.S. Pat. No. 4,211,586 discloses a method of forming a multicolor light-emitting array of diodes. The diodes are formed by differentially etching a graded n-type semiconductor and diffusing a p-type dopant into the surface of the n-type semiconductor to form a p-n junction diode.